In radiosurgery or radiotherapy (collectively referred to as radiation therapy) very intense and precisely collimated doses of radiation are delivered to a target region (volume of tumorous tissue) in the body of a patient in order to treat or destroy tumors or other lesions such as blood clots, cysts, aneurysms or inflammatory masses, for example. The goal of radiation therapy is to accurately deliver a prescribed radiation dose to the tumor/lesion and spare the surrounding healthy tissue. The geometric accuracy of patient positioning relative to the treatment beam, as well as the location and amount of dose delivered to the patient is therefore important. There are a number of factors that could affect geometric and dose delivery accuracy, such as, incorrect patient alignment relative to the treatment beam, misalignment of the light field versus radiation field, shift of the skin marker, patient movement, etc.
Because the radiation dose amount and dose placement need to be sufficiently controlled for accurate patient treatment, the radiation therapy machine itself needs to be properly tuned at the outset (on the production floor), and then continuously monitored through periodic checks, such as, during initial installation or during routine usage of the machine by the customer, to ensure that the system is operating within appropriate and expected parameters and standards.
Electronic portal imaging devices (EPIDs) were previously introduced to verify patient position. Thus, their primary use was for patient localization via portal imaging. However, due to their online efficiency and data density, portal imagers/MV EPIDs have also received attention as quality assurance (QA) devices. More recently, EPIDs have been employed for a variety of applications, including patient dosimetry and quality assurance (QA), to verify the treatment beams. Thus, the EPIDs have applications as imaging devices in machine-specific and patient-specific quality assurance (QA) and commissioning and calibration processes.
With the potential benefits of high data density and high resolution for EPID-based QA, there are also inherent problems associated with EPID quality assurance (QA). For example, EPIDs are relative measurement devices, convoluting the response variation due to radiation beam and per pixel characteristics (sensitivity, gain). Thus, the raw EPID images cannot be used to assess radiation beam characteristics. To differentiate between contributions due to radiation beam and per pixel characteristics complex calibration procedures are required. Also the pixel characteristics may vary over time, requiring frequent recalibration.
Currently existing EPID calibration processes try to correlate the measurement of an absolute external measurement device, for example a water phantom, with the EPID image, thereby isolating the contributions of beam and pixels. However, EPIDs are not dosimeters, as the interactions of photons leading to an EPID image is different than the interactions in water or tissue that lead to a radiation dose. Thus, the raw EPID image is not a dose image, and the EPID response deviates from what would be expected based on water-based dose measurements. As such, direct correlation is not possible.
Thus, the ease of using EPIDs makes them attractive for quality assurance (QA) applications, but the images must be corrected for non-linear behavior of the electronics and inhomogeneous pixel sensitivities. Further, in order to use an EPID for measuring energy change, beam alignment, and beam tilt relative to the collimator rotation axis, elaborate calibration procedures need to be implemented to calibrate the EPID's response to the measured values.
There is, thus, a need for an alternative approach to the extensive calibrations procedures currently applied that is independent from external dosimeters and from simulations, and a need for methods, systems, and devices by which EPIDs can be used as measurement devices for beam characteristics as well as for beam alignment without having to implement elaborate calibration procedures.
Further, since many of the modern radiation treatment devices, such as medical LINACS, are equipped with electronic portal imaging devices (EPIDs), there is a need for being able to use the EPIDs as beam alignment measuring devices without extensive calibration protocols in place, in order to be able to perform automatic calibration, tuning, and verification of the radiation treatment systems and devices. Since currently available radiation therapy machine tuning, calibration, and verification protocols are slow, inaccurate, require external hardware, and/or rely on subjective human decisions, employing EPIDs without complex calibration procedures, as disclosed throughout the specification, reduces overall costs, processing, and analysis time, as well as remove operator dependency.